Blind spot warning systems in vehicles may selectively display a graphic representation (ICON) as an indicator of a particular condition of operation. For example, a highly visible optical signal may be generated in a rearview mirror to indicate the presence of a vehicle in a blind spot, or other hazardous condition. Further, turn signal indicators in mirrors, or in the vicinity of mirrors, have been utilized for several years in vehicles. In some systems a warning signal is generated in such a way that the visible light is not in the rearview mirror, but in the interior of the vehicle, for example in the pillar or other location in general proximity to the mirror.
Human factors and ergonomic considerations provide some motivation for the design of blind spot and other warning systems. Also, enhanced warning systems can improve overall vehicle functionality, increase safety, and provide ease of use.
Technology advances in imaging and sensor technology have stimulated developments of improved warning systems. CCD cameras mounted on the car and on-board video image processing have been demonstrated. The field of view of a blind spot monitoring system need not be restricted to the vehicle's blind spot, but can also cover adjacent regions. The warning to the driver from the system can be any combination of visual, audible and/or tactile signals.
Existing blind spot warning displays generate a highly visible optical signal when a hazard is detected but can also impair visibility of the scene in the OFF-state (no hazard detected). Ideally, when in the OFF-state only the scene, viewed as a reflected image in the mirror (e.g.: a mirror image), should be visible. The ICON and any structure associated therewith should not impair visibility of such a mirror image. However, the structure of a conventional blind spot warning system ICON can cause reduced reflectance, light scattering, multiple reflections, ghost images, or similar optical phenomena. For example, in various designs the ICON, and the corresponding indicator region about the ICON, may be less reflective than the rest of the mirror.
Some existing blind spot warning indicators use an LED array to form an ICON, the array being mounted behind the mirror. The reflective coating of the mirror is removed from the region around the ICON to pass the optical signal radiation from the LED array. Thus, the effective mirror area is reduced and the indicator structure obscures any image that might be in or around the ICON region. Thus, when used in a rearview mirror, the visibility when in the OFF condition presents some limitations, including a viewing tradeoff.
Additionally, tradeoff(s) exist between the size and/or number of ICONs. A large ICON can further reduce the useful viewing area of the mirror, effectively introducing a blind spot in the mirror. Thus, the ICON area is often constrained. The ICONs in the mirrors of conventional blind spot warning systems are also relatively small and placed along the edges of the mirror in order to avoid obstructing the image of any object to the side of the vehicle. Notably, objects in the vehicle's blind spot are, by definition, not visible in the mirror. Such limits on the available locations and the small size can make ICONs more difficult to see and interpret. Furthermore, in some implementations multiple ICONs could be beneficial, but shape discrimination can be limited by the small size of the ICONs selected to reduce the obstructed area of the mirror. ICON locations are generally restricted to regions of the mirror that are not expected to show important information. However, it is still possible that useful and important information may be projected in this obstructed part of the mirror.
Information regarding vehicle warning technologies is readily available from several manufacturers, such as brochures or web-based videos. For example:
www.mazdausa.com/MusaWeb/displayPage.action?pageParameter=modelsMain&vehicleCode=CX9#/videos/safety;
http://www.ford.com/technology/;http://www.muthco.com/;http://www.cadillac.com/2011-escalade-suv/exterior-photos.html#item04;
www.acura.com/Features.aspx?model=MDX&modelYear=2011&context=Exterior#blind_spot_information_system; http://www.youtube.com/watch?v=5Te-WiRohR8; http://www.gizmag.com/go/2937/; http://www.volvocars.com/us/sales-services/sales/DocumentsNolvo-MY12-XC70-Brochure.pdf;http://www.smartmotorist.com/motorist-news/advanced-system-to-adjust-blind-spot-mirror.html
U.S. Pat. No. 7,008,091, entitled “Electromagnetic radiation assembly”, and U.S. Patent Application Pub. No. 2008/0218871 entitled “Mirror assembly” relate, among other things, to rearview mirror based warning systems for use in vehicles. Automotive Engineering International, Sep. 20, 2011, pgs. 12-17, “Advancing optical films” (adapted from Bastawros et al.) discloses and compares various display technologies with potential use in automotive displays, including polycarbonate films with engineered microlens surface structures to control illumination uniformity.